Getting Valves Right on an SBC 350
The firing order on these engines is 1-8-4-3-6-5-7-2, but the actual valve adjustment sequence is different. Most people mix those two up and waste an hour twisting wrenches back and forth. Once you know the sequence, it takes about twenty minutes with the engine at operating temperature and the rocker cover off. Here's the actual order you use when the engine is hot and idling. You start with cylinder 1, then move in this pattern: 1, 2, 6, 4, 8, 5, 3, 7
The number next to each cylinder tells you which valves to adjust. When you are at cylinder 1 in the sequence, both the intake and exhaust valves on that cylinder are set. Then you move to cylinder 2 and do the same. When you reach cylinder 6, you are adjusting one cylinder while cylinder 1 is still at top dead center on its compression stroke. This is where people get confused, so pay attention here. Cylinder 1 is at TDC compression stroke. You adjust all valves on cylinder 1. Then rotate the crank one full revolution to bring cylinder 2 to TDC compression, and adjust all valves on cylinder 2. From there, you jump around the sequence because each position takes advantage of the valves that are both closed at the same time due to the cam profile and firing order. The numbers in the sequence above represent the cylinder you are currently setting at TDC compression stroke. At each stop, you adjust every valve on that cylinder. That gives you a complete valve job in eight stops, not sixteen. If you are adjusting cylinder by cylinder through the firing order, you are doing it wrong and will either miss valves or set them while they are open.
I ran into a specific problem a few years ago on a '78 block that had been rebuilt twice before I got it. The previous shop used the firing order as the adjustment sequence, which left two cylinders off by a full cam revolution. The engine ran rough at idle, had a slight miss under load, and I couldn't find it because the valve lash felt fine on paper. What actually happened is that the exhaust valves on cylinders 3 and 5 were being adjusted while they were still opening and closing, so the hot lash was wrong. I caught it by doing a vacuum gauge test at each cylinder, running a hand over each exhaust manifold runner while the engine was at idle, and noticing runner three and five were significantly hotter than the others. That confirmed the valves on those cylinders weren't seating properly. I stripped the heads again and redid the adjustment using the correct sequence. The misfire went away immediately and idle vacuum stabilized from 14 to 17 inches of mercury.
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How the Adjustments Actually Feel
When you have the right clearance, the rocker arm has just enough play that you can feel a slight wiggle when you push and pull on the valve stem with your fingers. The feel is not loose. It is not binding. It sits somewhere in the middle where the valve train stays quiet at operating temperature but still closes fully when cold. Intake clearance on a stock SBC 350 is typically 0.010 to 0.012 inches when cold. Exhaust is 0.012 to 0.014 inches cold. These are base specs. If you have a solid lifter cam with any real duration, the exhaust clearance needs to be on the tighter side because exhaust valves run hotter and expand more. A big cam on stock rocks will want 0.012 on intake and 0.010 on exhaust when cold. Go too tight and you will burn valves. Go too loose and you lose lift at speed. The pushrod tubes in some later blocks interfere with the wrench angle on the exhaust side of bank two. I had to use a flex-head ratchet and a 3/8 drive box end wrench with a six-point crown on the nut. The twelve-point rounds off in about ten adjustments if you are not careful. Use six-point every time. The difference is less than two minutes of stripped nut removal per bank, but it adds up fast.
What Happens When This Method Breaks Down
The sequence method assumes your timing is correct. If the distributor is installed one tooth off, or the cam is walking on the crank, the sequence still works mechanically but your valves will never be set correctly because the pistons won't align with the cam lobes at true TDC compression. Always verify timing with a degree wheel or at minimum check that number one is on compression stroke with the harmonic balancer marker aligned and the #1 intake and exhaust valves both loose when you rock the piston. If you have hydraulic lifters and the engine is ticking, valve adjustment is not the fix. The issue is usually sticky pushrods, a clogged oil galley in the head, or lifters that have lost their bleed-down control. I pulled the pushrods on a 350 that had been misadjusted twice by different shops because the mechanic kept chasing noise that was actually a collapsed lifter on cylinder seven. The valve was gapped correctly but the lifter was empty. Bleeding a hydraulic lifter in place is finicky. Removing the head and bench-bleeding them took thirty minutes and stopped the tick permanently. Another common failure point is people adjusting valves while the engine is cold on a hot engine that has been sitting. The aluminum head and steel pushrods expand at different rates. If you set hot clearance with a cold engine, you will have the same symptoms as an over-tight setup: poor idle, low compression, and valve float at high rpm. Always warm the engine to normal operating temperature before setting valves on an aluminum-headed SBC.
Tools and Setup
You need a feeler gauge set with 0.010, 0.012, and 0.014 blades minimum. Some people prefer a dedicated valve adjustment gauge like a .012 inch adjustable gap tool because it is faster and less error-prone than sliding feeler gauges in and out under load. The feeler gauge method works fine if you are careful. Slide the gauge between the rocker tip and valve stem while applying light pressure to the rocker. It should drag slightly. Not slip through freely. Not require force to push in. A timing light is not required for valve adjustment, but a timing tape or pointer on the harmonic balancer makes finding TDC compression stroke significantly faster than rotating by ear. A helper who can call out when the piston hits TDC and both valves on cylinder one go slack is worth having if you are alone. I usually just watch the #1 intake valve with a borescope through the spark plug hole until my eyes got better at judging rock movement. The exhaust manifolds on these blocks are the real bottleneck. Bank two exhaust pushrods are almost always tight to access because the manifold tunnels run close to the head. If you have tubular headers bolted on, bank two takes half the time. If you still have the stock iron manifold, budget extra time and be prepared to remove the EGR tube on many late-model blocks. The EGR crossover blocks the path to three of the exhaust pushrods on that side unless you take it off.
